From: Antonin Houska <ah@cybertec.at>
To: Tomas Vondra <tomas@vondra.me>
cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
    vignesh C <vignesh21@gmail.com>,
    Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
    Amit Kapila <amit.kapila16@gmail.com>,
    Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
    Matthias van de Meent <boekewurm+postgres@gmail.com>,
    Pg Hackers <pgsql-hackers@lists.postgresql.org>,
    Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
In-reply-to: <1c197f2d-49a2-4830-8dde-55867218b62d@vondra.me>
References: <202604060918.qw5ms7cbr2hz@alvherre.pgsql>
 <1c197f2d-49a2-4830-8dde-55867218b62d@vondra.me>
Comments: In-reply-to Tomas Vondra <tomas@vondra.me>
   message dated "Wed, 08 Apr 2026 12:20:53 +0200."
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Date: Wed, 08 Apr 2026 12:46:46 +0200
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Tomas Vondra <tomas@vondra.me> wrote:

> while building on a rpi5 with a 32-bit system, I'm getting these warnings:
>=20
> config.status: linking src/makefiles/Makefile.linux to src/Makefile.port
> In file included from ../../../src/include/access/tupmacs.h:20,
>                  from ../../../src/include/access/htup_details.h:20,
>                  from ../../../src/include/access/relscan.h:17,
>                  from ../../../src/include/access/heapam.h:19,
>                  from repack.c:36:
> In function =E2=80=98VARSIZE_ANY=E2=80=99,
>     inlined from =E2=80=98restore_tuple=E2=80=99 at repack.c:2731:15:
> ../../../src/include/varatt.h:243:51: warning: array subscript
> =E2=80=98varattrib_4b[0]=E2=80=99 is partly outside array bounds of =E2=
=80=98union
> <anonymous>[1]=E2=80=99 [-Warray-bounds=3D]
>   243 |         ((((const varattrib_4b *) (PTR))->va_4byte.va_header >>
> 2) & 0x3FFFFFFF)
>       |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
> ../../../src/include/varatt.h:467:24: note: in expansion of macro
> =E2=80=98VARSIZE_4B=E2=80=99
>   467 |                 return VARSIZE_4B(PTR);
>       |                        ^~~~~~~~~~
> repack.c: In function =E2=80=98restore_tuple=E2=80=99:
> repack.c:2717:49: note: object =E2=80=98chunk_header=E2=80=99 of size 4
>  2717 |                         }                       chunk_header;
>       |                                                 ^~~~~~~~~~~~
> In function =E2=80=98VARSIZE_ANY=E2=80=99,
>     inlined from =E2=80=98restore_tuple=E2=80=99 at repack.c:2734:4:
> ../../../src/include/varatt.h:243:51: warning: array subscript
> =E2=80=98varattrib_4b[0]=E2=80=99 is partly outside array bounds of =E2=
=80=98union
> <anonymous>[1]=E2=80=99 [-Warray-bounds=3D]
>   243 |         ((((const varattrib_4b *) (PTR))->va_4byte.va_header >>
> 2) & 0x3FFFFFFF)
>       |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
> ../../../src/include/varatt.h:467:24: note: in expansion of macro
> =E2=80=98VARSIZE_4B=E2=80=99
>   467 |                 return VARSIZE_4B(PTR);
>       |                        ^~~~~~~~~~
> repack.c: In function =E2=80=98restore_tuple=E2=80=99:
> repack.c:2717:49: note: object =E2=80=98chunk_header=E2=80=99 of size 4
>  2717 |                         }                       chunk_header;
>       |                                                 ^~~~~~~~~~~~

> I'm not sure if it's just the compiler (gcc 14.2) being pesky, or if
> it's an actual issue. The repack tests seem to pass fine.

We already introduced this definition above in the function to suppress this
kind of warning

    union
    {
	    alignas(int32) varlena hdr;
	    char		data[sizeof(void *)];
    }			chunk_header;

The problem on a 32-bit system probably is that sizeof(void *) is 4. We need
some other constant. Maybe (sizeof(varlena) + 1) ...

Thanks.

--=20
Antonin Houska
Web: https://www.cybertec-postgresql.com